Detailed temperature measurements on different platforms

Note:* All temperatures in degrees Celsius. All thermal tests made
with PCB version EDA-02267-V5-0.

Test environment

- VME: Wiener and Elma crates, with up to 7 SVECs (14 Fine Delays)
installed in subsequent slots. Whenever possible, different
combinations
of VME slots and fan speeds were used. All crates used a MEN A20
controller. Ambient temp 26-28.

- Temperatures were logged over time to make sure they have settled up
before taking measurements. The first stable sample (with less than 1
degree temperature change over 1 minute) was used for the statistics.

- Unused slots were covered to ensure maximum airflow through the
FMCs.
- PXI Express: National Instruments crates with the SPEXI and a Fine
Delay: 4-slot (PXIe-1071) at ambient temp 25C and 8-slot (PXIe-1062Q) at
ambient temp 29C with one Fine Delay in different slots.

Replacing the LVPECL delay lines with LVDS counterparts

We tried replacing the SY89295 chips (and their LVPECL terminations)
with an LVDS version: ICS854S296I-33. Temperature test
(identical conditions) performed on a SVEC showed 5 degrees less on the
modified card:

new delay line (LVDS) 51.31 Celsius

old delay line (PECL) 56.38 Celsius

Note that the EDA-02267-V6-0 PCB is not foreseen for the LVPECL
termination resistors for the new delay line chip. In case we decide to
use the new chip, for production purposes a new revision of the PCB
should be made. Also, the new LVDS delay line is much harder to obtain
than the PECL version.

Fitting a fan on SPEC/Kontron PCs

We tried fitting a small fan below the FMC in the cutout on the SPEC
card. The fan is installed on a mechanical support made from FR4 and
attached to the board using the FMC's mounting screws. The fan design is
available here

Capacitor temperature

Electrolytic capacitors lifetime is the most important failure factor
caused by high operating temperature. We measured the temperatures of
the capacitors:

using a thermal vision camera

by gluing the DS18B22 sensor directly over the hottest capacitors.

We found out that the worst capacitor temperature was around 75 degrees
C, while the board's temperature was 89 degrees C, that is, 14 degrees C
of difference. *For the temperature (as measured by the normally placed
onboard sensor) of 65 degrees C, it means the capacitors are never
hotter
than approx. 51 degrees C.*

The photo below shows the temperature distribution on the board (note
the temperatures are much lower, because the card is placed outside a
crate on an extender cable, thus getting better
ventilation).

Conclusions

What to do:*

Don't use heatsinks.

Elma crates. Set air flow to maximum level. Do not use slot 6 on
Elma 3U crate.

Wiener crates. Set air flow to medium/maximum level.

Kontron PCs must be equipped with additional fan units.

Notes/observations:*

Heatsink is not effective if the air flow is too slow. In such
case, the heat is exchanged through radiation with the cards in
immediate neighbourhood, causing collective heating of all
mezzanines/carriers (the ones in the middle are the worst).

Forced airflow is absolutely necessary. Set the fans to the
maximum level in all VME installations.

Using an LVDS delay line chip gives little thermal advantage.

Cards in the middle slots (8-10) are the worst (25 degC difference
over slots 7 and 12). This suggests uneven air flow in the crate.

FMC1 is approximately 8-10 degrees cooler than FMC2 in 3U and 1U
crates (opposite on Wiener/big Elma). FMC1 is closer to the fans and
obstructs air flow to FMC2.

Large temperature spans in VME crates suggest uneven air flow
between different slots.

On Elma 6U and Kontron PC platforms, the temperatures are
unacceptable and exceed the components rating (-40 ... +85).

Not using slot 6 on Elma 6U, only on Kontron PC platforms, the
temperatures are unacceptable and exceed the components rating (-40
... +85).
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